Coaxial magnetron with improved starting

Abstract

The cathode of a coaxial magnetron has a cylindrical electron emitter with a radially extending projection which is asymmetrical with respect to the axis of the emitter. The projection suppresses starting of the magnetron in the TE 121 mode and reduces starting jitter. In a preferred embodiment, the projection is in the form of a circumferential ridge extending around approximately one-half the circumference of the cylindrical surface and is centrally located thereon. The projection is oriented at 45 degrees with respect to the output of the magnetron. The power output of the magnetron is not substantially reduced.

What is claimed is: 
     
       1. A crossed field electron discharge oscillator comprising: cathode means for generating a stream of electrons, including an electron emitter with a generally cylindrical surface having at least one radially extending projection which is asymmetrical with respect to the axis of said cylindrical surface;   a vacuum envelope for maintaining a vacuum about said stream;   microwave circuit means for supporting electromagnetic fields in interactive relationship with said stream of electrons;   means for coupling electromagnetic wave energy from said circuit means;   means for applying an electric field between said cathode means and said circuit means; and   means for applying a magnetic field perpendicular to said electric field in the region of said stream, said projection on said electron emitter being operative to enhance starting of said oscillator in a desired mode without substantially reducing the power output of said oscillator.   
     
     
       2. The oscillator as defined in claim 1 wherein said projection is in the form of a circumferential ridge on said cylindrical surface. 
     
     
       3. The oscillator as defined in claim 1 wherein the surface area of said projection is less than 20% of the surface area of said cylindrical surface. 
     
     
       4. The oscillator as defined in claim 2 wherein said ridge extends around less than the full circumference of said cylindrical surface and is tapered to zero thickness at its ends. 
     
     
       5. The oscillator as defined in claim 4 wherein said cathode means and said circuit means define therebetween a toroidal interaction space and wherein said projection extends radially into said interaction space by about 10 to 20 percent of the radial dimension of said interaction space. 
     
     
       6. The oscillator as defined in claim 4 wherein said means for coupling electromagnetic energy from said circuit means includes stabilizing cavity means coupled to said electromagnetic fields of said circuit means and an output coupling iris for coupling electromagnetic fields from said cavity means and wherein said projection is oriented at an angle of about 45 degrees with respect to said iris. 
     
     
       7. The oscillator as defined in claim 6 wherein said ridge is axially centered on said cylindrical surface. 
     
     
       8. The oscillator as defined in claim 1 wherein said projection on said electron emitter is adapted to suppress starting of said oscillator in a TE 121  mode.